Lipsticks are primarily made of lipophilic or hydrophobic materials. Lipsticks designed for providing a moisturizing benefit to the lips further contain water, polar solvents, or other moisturizing components which are more or less hydrophilic. The use of association structures have been suggested to bind such moisturizing components in the lipophilic matrix of the lipstick. While such lipstick compositions provide a favorable moisturizing benefit to the lips, they were not completely satisfactory in terms of physical stability, color stability, and sweat resistance.
Physical stability relates to the stability of the stick during storage and upon use. For example, a stable stick does not deform during storage at ambient temperature, and does not bend or break upon normal condition use. Color stability relates to the stability of color during storage and after applied on the lip. It has been known that lipsticks containing a high amount of moisturizing components have the tendency to change color over time after applied on the lip. Sweating is a phenomena seen on the surface of sticks, and is believed to be due to oils and/or solvents separating and leaking out of the lipophilic matrix of the stick. Sweating provides a negative appearance to the user.
Emulsion compositions utilizing cholesteryl derivatives and swelling clay material are disclosed, for example, in Japanese publication A-8-20529. While such emulsion is believed to provide physical stability to the composition, further improvement is desired.
Based on the foregoing, there is a need for a lipstick composition which has improved physical stability, improved color stability, and improved sweat resistance, while also providing moisturizing benefit to the lips. There is also a need for a personal care composition which has improved physical stability over a wide range of viscosity and/or hardness.